Classifier



Nov. 29, 1949 A. c. MUNRO, JR 2,489,661

CLASSIFIER 2 Sheets-Sheet 1 Filed April 29, 1946 O a O o o o o O o o o OgO 0o EQ q-J '6 IN VEN TOR.

A. c. MUNRO, JR 2,489,661

CLASSIFIER 2 Sheets-Sheet 2 '3 N N INVENTOR. Alexander QMzmr'oJi' flyv/ I Arrow I IIIIIIIIIIIIIII Nov. 29, 1949 Filed April 29, 1946 Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE CLASSIFIER Alexander Munro; 'r'., Los Angeles, Calif; Application April 29-, 1946;.Serial .No; .665,703 6 Claims; (01. 209-464) This. invention relates to classifiers in whichsolid particles are suspended ina body of liquid,. usually water, in which the. particles are separated by settling actionaccordingto size. The coarser solids, commonly referred to assands, which-settle out of the liquid, are removed therefrom by mechanical means, while. the finer. particles; commonly referred to asfines oroverfiow. product, are left in suspension to'be carried away with the'liquid, usually by means of .an overflow launder. Such classifiers are commonly used-in handling ores during; metallurgical operations, being frequently operated in closed-circuit with a ball mill or other grinding apparatus, but it will be understood-that ent invention may beused for any desired purpose where the: classification. of solid materials ac. cording to size-is desired.

The-present invention is concerned particularly with classifiers of. the belt drag, type, in.which settled-coarser solids or sands areremovedafrom-l the'bottom of theclassifier tank by means-of an: endless belt provided with drag blades or rakes which drag the settled solids upward along an inclined bed or deck to apoint of discharge above: the =liquid' level.

One ofthe principal objects ofv theinvention; is -to-provide a. belt drag classifier which-w-ill-produce amore effective classifying actionthan belt drag classifiers heretoforeemployed.

Another important object is toprovide a--.c1assi-* fier of relativelylow: cost, both in its construction and also in itsoperationand maintenance:

A further object is to provide a belt drag classi' fier inwhich the belt may be made oflany desired width to obtain the desired 1 capacity,v withoutv adversely affecting the classifying action;

A further object is to-providea drag classifier capable of elevating the settled coarse-solids,-.or sands, along an inclined bedof steepersl'op'ethan other types of classifiers,- whereby the sands may" be raised to the height requiredin la-rge closedcircuit ball mill-classifier installations inaclassi fier of moderate" length and without requiringthe use of auxiliarypumping equipment.

A further object isto' provide a drag classifieremploying'a belt provided with .rakesfor-elevat ing-sands along'an inclined bed, inwhich-a sub stantial portionr of the sands arecarriedout of the liquid" body or pool on the. surface: of the belt, thereby reducing the dr-ag load: on theirakes, and inwhich the sands carried by the belt are washed therefromafter leaving the mainsettlingm zone in such manner as to-provide-a high ca-- pacity together with highly effective classifica-- tion.

A further object is to providea belt=drag classifier in which the rakes operate at: arelatively greatdepth in: arelatively extended. settling: zone-,withoutrequiringtheruse of an :underrwatenr the-classifier of the pres? andfwithout requiringthe provision-ofany mechanism for lifting the rakes under such conditions.

A: further object is to eliminate the necessity of. providing belt-tensioning means for maintainingthe=belt tight on the pulleys.

A.further object is to provide a belt drag classifier: in which wear on the rakes or scraper blades is reduced to aminimum.

In. accomplishing the above objects, as well.

asother. objects-whichwill be pointed out hereinafter or will be evident from the following description, I employ for the purpose of removing the .settled'solids or sands an endless belt which isprovided with scraper blades or rakes for draggingsuch'solids. upward along the inclined the tank, and which isalso provided with a multiplicity of perforationsv bottomawall or deck of distributed over thesurface of the belt, and I provide water spray means for supplying water to the-upper surface of the-lower run of the belt, after thebelt has left the liquid for the purpose the upper surface rations. In the-preferred embodiment of. the invention, the belt is not kept under tension soas to extend substantially straight between thei-pulleysandthe weight of the belt and rakes,

together with. settledsolids accumulating on" the. lower runof the belt,- causes the lower run to so-that the belt extends almost sag; appreciably, horizontal" orslopes upward ver-y gradually for some distance'afterleaving the tail pulley, and the slope increases progressively toward the'sands discharge end of the. tank. Furthermore, the

overflow launder is preferably located at aposition between the two-pulleys over which the belt runs, at-aposition substantially above the lowest point ofthebelt.

The accompanying drawings illustrate a preferred form ofi classifier according to the present invention, and certain possible modifications:

thereof. Referring to these-drawings? Fig. 1- is a plan view, run of the belt broken-away, showing a preferred formof classifier according to this invention;

Fig. 2-isasomewhat' enlarged'plan view of a portion of: the lower run of the belt;

Fig, 3 lea-transverse sectional view on line rakes;

body or pool, of washing settled solids fromof the'belt through said perfowith parts of the upper.

3---3 in.Fig-, 2, showinga preferred construction of the Fig. 4 is a transverse sectional view on line 44 in Fig. 2, showing one of the rakes provided with a serrated lower edge for a purpose described hereinafter;

Fig. 5 is a longitudinal section of a portionof the belt, taken on line 55 in Fig. 2;

Fig. 6 is a vertical section of the classifier, on line 66 in Fig. 1;

Fig. 7 is a partial vertical sectional view of a modified form of classifier; and

Fig. 8 is a partial longitudinal section of the belt, corresponding to Fig. 5 but showing a modifled arrangement of the perforations in the belt.

The classifier shown in Figs. 1 and 6 comprises a tank adapted to contain a body of liquid, generally water, having a bottom' wall I, side Walls 2 and an end wall 3. Side walls 2 and end wall 3 extend upward above the liquid level indicated by the dot-dash line at L. The bottom wall I is inclined upward in a direction away from the end wall 3, through the major portion of its length, to provide an inclined deck D which extends from a position below the body of liquid to a position of sands discharge a considerable distance above the liquid level at the opposite end of the tank, as indicated at 4.

A continuous flexible belt 5 of rubber, rubbercovered fabric, or other suitable belting material is mounted for movement through the tank and is carried on a head pulley l and tail pulley 8, whose shafts are rotatably journaled in suitably mounted bearings 9 and Ill, respectively. The

belt 6 is preferably mounted slackly on pulleys 1 and 8, and said pulleys are preferably crowned somewhat as shown at 1 and 8' in Fig. 1 to maintain the belt in properly centered position thereon. Belt 5 is driven by means of head pulley I which is operated by any suitable motive power such as an electric motor I I connected thereto through conventional speed-reducing mechanism indicated generally at I2 and I3. The driving pulley l is preferably slotted, as indicated at I4, so as to prevent slipping of the belt thereon.

The tail pulley 8, which acts as an idler pulley, is of relatively large diameter and extends to a position substantially below the liquid level and near the bottom of the tank, above and adjacent the lower end of the inclined deck D, while head pulley I is of' smaller diameter and is located at a higher level, above and adjacent the upper end of said deck, so that the lower run of the belt indicated at 6a extends from a position near the bottom of the tank at the deeper portion thereof, in a generally upwardly inclined direction, to a position above the liquid level and beyond the sands discharge lip 4. The upper run of the belt, indicated at 62), is disposed wholly above the liquid level in the tank.

Belt 6 is provided with a plurality of equally spaced outwardly projecting rakes I6 extending transversely and secured to the outer surface thereof at suitable intervals. In the lower run Ga, these rakes project below the belt, in position to scrape or drag settled solids upwardly along the inclined deck as the belt is moved in the direction indicated by the arrows at A in Figs. 5 and 6. Said rakes extend across substantially the entire width of the belt and may project somewhat beyond the edges thereof as indicated at Ilia. Each of said rakes, as illustrated particularly in Figs. 2, 3 and 5, may comprise a length of angle iron I! bolted or otherwise secured to the belt and having its middle portion bent outward as shown at I'Ia to conform to the crown of the pulleys. The rakes are preferabl provided with wearing blades or tips I 8 removably secured thereto and projecting outward beyond the outer edges of the angle bars. As illustrated in Fig. 3, I prefer to provide a plurality of such removable wearing blades for each rake, bolted or otherwise secured to angle bar ii in end-toend relation, with their outer edges disposed in a straight horizontal line.

In order to reduce wear on the removable wearing blades, I prefer to provide one of the rakes, indicated at IS in Figs. 2, 4 and 5 with wearing blades I8 having serrated edges I9 which extend beyond the edges of the other rake blades to prevent the'sands from becoming unduly hardened, as described hereinafter. More than one of the rakes may, if desired, be thus provided with a serrated edge, but I have found that the provision of one of these serrated-edge blades at any position on the belt is generally suflicient for this purpose.

Belt 6 is of suificient length, in relation to the spacing of the pulleys, to sag appreciably between said pulleys. The weight of the belt and the rakes I6, together with the sands deposited thereon as hereinafter described, causes the lower run of the belt, even though submerged beneath the liquid and subjected to an upward thrust against the rakes by the solids depositing at the bottom of the tank, to sag so that it extends almost horizontal or even slopes slightly downward after leaving the tail pulley 8 and then slopes upward, at first very gradually and then at a progressively increasing angle toward the head pulley 1. It will be seen that, because of this sagging of the belt, said belt and the rakes carried thereby are caused to follow a curved path through the tank and are submerged to a relatively great depth in a relatively extended settling zone adjacent the tail pulley and at the side thereof toward the inclined deck D.

It will also be noted that the deck D is located 10w enough to accommodate the sag of the lower ruin of the belt, said deck being disposed below the curved path of the rakes I6 resulting from the sag of the belt, and being preferably shaped to conform generally to the curvature of the belt. Thus, the upper portion D2 of the deck is shown as inclined at a steeper angle than the lower portion D1. From the lower end of deck portion Dl, which is adjacent the lowermost point of the belt, the bottom wall I is preferably inclined slightly upward, as shown at I a, to the end wall 3.

The classifier tank is provided with a transversely extending feed launder 2| which is shown as located above the end wall 3 at the deeper end of the tank, a transversely extending overflow launder 22 located between the pulley B and the sands discharge end of the tank, and a transversely extending sands discharge launder 23 positioned to receive the sands discharged over lip 4. The overflow launder 22 is provided with side walls 22a whose upper edges extend horizontally across the tank and serve to establish and maintain the desired liquid level therein.

It will be seen that said overflow launder is located within the above-mentioned relatively deep extended settling zone afforded by the sag of the belt, and is above the lower portion of the lower run of the belt. The effect of the sag of the belt in increasing the depth of the settling zone at the position of the overflow launder may be seen by a comparison with the depth of settling zone that would be afforded if the belt extended straight between the pulleys, as indicated by the dot-dash line at X in Fig. 6 and the lower z rsaeer edges otthe rakes moved along theecorresponding; straight. path indicated at :Y;

The-belt. leis provided with avpluralityof perforationsor openings extending therethrough and-distributed over its surface. Said-openings may be-of any desired size and shape: Circular openings-about 1" tO'l /z" in diameter have been found satisfactory'. These openings may be ar-- ranged. transverserows, and I have shown a pluralityof such rows between each two adjacent rakes, as best illustrated in- Figs-. 2;and 5. The number. and total area of the perforations may be selected. to give the best resu1ts,.butiI- have found-that the total area of perforations should generally be between about 5% and about of;the total area of the-belt (including the per-' forations) and-preferably in theneighborhoodof 8% to 12% ofthe total belt area.

Suitable. means are provided for supplying water or other liquid,. preferably in the'form'of sprays, onto the --upper surface of the lower run oibeltl at a position above the point-where the belt emerges from the body of liquid, that-is; ata position abovethe liquidilevel L.

Said liquid supply means may comprise, for example, one or more spray pipes or headers'extending transversely above the lower run of the belt, atone or more positions above the; liquid level. In the drawings I have'shown a pipe. 21 extending across the entire width of the beltand above; the upper: run thereof at a position above; and closely adjacent the point. at which the'belt emerges fromthe liquid,- and another pipe. 28 extendingacross andabovethe belt at aposition further along the. path thereof; each ofsaid pipes being: provided with a plurality of spacedopen-- ings as indicated at 2'! and 28 respectively; so

positioned and directed as todeliver water sprays in ageneral direction inclined downwardly and rearwardly with respect to the: direction of. belt. travel. The water sprays. deliveredby'these pipes are indicated in dotted li-nesat za-and-tmrespectively, and .I have. shown the pipe 2.1. asprovided. with a larger number. of spray openings-or orifices than the pipe as. Pipes 2.! and-28 areshown connected through control valves-toa pipe 31 for supplying water or other liquid thereto; The individual valves. may be adjustedto any desired quantity of liquid to the respective pipes.

While this particular arrangement and-100a tion. of; spray pipes, has-been found advantageous; it is not essentialto the present invention. In some cases I. may use. only a-single spray pipelocated ateitherof the two positions-shown or atv any other. desired position betweenthe point wherethe. belt. emerges: from the liquid and the.- sands. discharge lip 4, or'I may provide any de-- sired number of spraypipes atdifferent locations within this. region.

In the. operation of the classifier described above the. feed, comprising solid. particles and liquid,.issuppliedthrough feed launderzl into the tank,. and the liquid eventually overflows the upper edges of the side walls 22a, of overflow launder 22; so as to mainta-in-inrthe tanl: a body of liquid up to the level indicated at L. Moderate agitation of the liquid and. suspended solid particles is provided by the movement of the drag beltsand tail pulley 8 through the liquid, but the. agitation so produced is not suffi'ciently active to prevent gravity: separationof thecoarser and finer particles by settling. action. The coarserparticles settle toward the bottom-oi the tank; this settling action taking place principally in the relatively extended settling zone of relatively great: depth in the. portion. of" the? tank; located;

settled solids, whence the solids are continually moved thereby 1 upwardly along the above said deck, outof the body ofliquid. After leaving the liquid the solidsremoved'by the rakes It and are are. movediby the rakes over the upper portion .of the-deckto permit draining of liquid therefrom back: into the. liquid body, and are delivered over:

the sands discharge-lip into the sands-discharge;

launder 23'.

Some of the coarser solids or sands which-are;- deposited onthe upper surface of the lower run ofthe belt are carried on the belt out oftherbody of liquid, and are thereafter washed from the'belt by'the liquid sprays from pipes 21' and 28; through the --p erforations and into the path of the rakes l5.- Thesesands are piokedup by the rakes'and' discharged thereby along with the other sands,

,while the-water from the sprays drains backint'o the pool in-the'tank'. The washing action of the sprays also tends todislodge any fine solid particles.- that may have been deposited with the coarser solids: on the belt, and such dislodgedfine,-particleswill-v tend to remain in suspension in. the liquid flowing down. over the deck, and will: thus be returned tothe-main body of liquid. Hence this washing action improves the separation-of coarse. and fine solids and-contributes tothe efficiency of classification. Ithasbeen found that a particularly efiective de-sliming action is obtained when the sands are washed from the upper surface of the belt at-a point just above the liquid pool, as by means ofthe liquid'sprays 29 from pipe 21.

Thefinesolids that remain in suspension in the liquid inthe settling zone are discharged with the liquid through the overflow'launder 2'2.

Itwill be noted that the belt 6. extends transversely the major portionof the transverse extent ofthe rakes it, and the total area of the perforations-zli is relatively-small ascompared to the total area thereof. Gonsequently, a' considerableproportioncf the coarser solids moving downward bygravity towardthe path of movement of the rakes are caught cnthe upper surface of .the belt and, are carried out of the liquid on the belt instead. ofbeing allowed to fall to the bottom of the tank. for removal by the dragging action of the rakes. Thisincreases the capacity of theclassifier andalsoreduces the drag load on the rakes; and also causes a considerable proportion of the coarse solids to be subjected. to the washaingactioniof the liquid sprays from pipes -21 and 'lfirwith: resultant improvement. in'the efficienc of. classification; as: noted above;

ln add-ition t'o the possible modifications in certain parts of the. apparatus; mentioned. above, numerous cthersinodificationsmay be made within-ztl'ie. scoperciv my invention. For-example; as illustrated. in: Fig. '7; the positions. of the feed launder and. fines overflowrlaundermay be reversed, In thiscase, theieed launder2l is shown as: extending'across thetankat the same side of pulleyti the inclined deck. D and between said pulley andnthe: sands discharge end of the machine. while the lines overflow launder 22 with: its-side wall: 22a which defines the liquid level-.inithe tank isz-located above: the; end; wall: 31

The other parts of the apparatus are the same as described above.

The rakes on the belt can be of any desired depth perpendicular to the surface of the belt, for example, from about three or four inches to about 10 inches or more. With relatively deep rakes, in which the flange of the angle bar secured to the belt may be relatively wide, it may be desirable to provide perforations in this angle flange and in the part of the belt to which it is secured, in order to provide more uniform distribution of the perforations over the entire surface of the belt. Such a construction is illustrated in Fig. 8, the perforations in the angle bar flanges and in the portions of the belt to which it is secured being indicated at 250, and 25b respectively.

By providing one of the rakes with a projecting serrated edge H), as described above in connection with Figs. 4 and 5, the teeth of this rake dig into and loosen the surface of the bed of settled solids on the deck D. This prevents formation of a hard or caked surface and thus reduces the wear on the edges of the rakes.

The weight of the rakes i6 is an important factor in contributing to the desired sag of the belt and maintaining the desired relatively great depth of pool in the settling zone (below the preferred location of the overflow launder as shown in Figs. 1 and 6) regardless of tonnage handled, or size or density of feed. The angle bars I! of the rakes may be extra heavy, for example, in installations handling a coarse high density feed, while lighter weight angles may be used when handling a fine feed of low specific gravity.

I claim:

1. In a belt drag classifier for separating solid particles suspended in a liquid, the combination comprising: a tank adapted to contain a body of liquid containing suspended solid particles, having a bottom wall providing a deck inclined upward in a direction away from one end of the tank to a position above the surface of said body of liquid; an endless belt having its lower run extending within said tank and movable upwardly along and above said inclined deck to a position above the body of liquid, said belt being provided with a plurality of transversely extending outwardly projecting rakes for moving settled solids upwardly along said deck; said belt extending ransversely the major portion of the transverse extent of said rakes and being provided with a multiplicity of perforations distributed over its surface; and means for supplying liquid to the upper surface of the lower run of said belt at a position above the body of liquid, to wash solids from said upper surface through said perforatio-ns.

2. In a belt drag classifier for separating solid particles suspended in a liquid, the combination as set forth in claim 1, in which the total area of said perforations is between about 5% and about 30% of the total area of the belt.

3. In a belt drag classifier for separating solid particles suspended in a liquid, the combination as set forth in claim 1, in which the total area of said perforations is in the neighborhood of 8% to 12% of the total area of the belt.

4. In a belt drag classifier for separating solid particles suspended in a liquid, the combination comprising: a tank adapted to contain a body of liquid containing suspended solid particles, having a bottom wall providing a deck inclined upwardly in a direction away from one end of said tank to a position above the surface of said body of liquid; an idler pulley extending within said tank above and adjacent the lower end of said inclined deck; a drive pulley located above and adjacent the upper end of said deck; an endless belt carried by said pulleys and having its lower run extending within said tank and movable by said drive pulley upwardly along and above said inclined deck to a position above the body of liquid, said belt being provided with a plurality of transversely extending outwardly projecting rakes for moving settled coarse solids upwardly along said deck; said belt extending transversely the major portion of the transverse extent of said rakes and being provided with a multiplicity of perforations distributed over its surface, and said belt extending slackly over said pulleys, whereby the weight of said belt and rakes causes the lower run of the belt to sag appreciably between said pulleys and to move in a curved path, and said deck being disposed below thecurved path of the rakes resulting from said sag of the belt so as to provide an extended settling zone of relatively great depth in the tank adjacent the lower portion of the lower run of the belt; and means for supplying liquid to the upper surface of the lower run of said belt at a position above the body of liquid, to wash solids from said upper surface through said perforations.

5. In a belt drag classifier for separating solid particles suspended in a liquid, the combination as set forth in claim 4, in which said tank is provided with means for supplying solid particles and liquid thereto adjacent said one end thereof, and with a liquid overflow launder extending above the lower run of said belt and within said ex tended settling zone.

6. In a belt drag classifier for separating solid particles suspended in a liquid, the combination comprising: a tank adapted to contain a body of liquid containing suspended solid particles, having a bottom wall providing a deck inclined upward in a direction away from one end of the tank to a position above the surface of said body of liquid; an endless belt having its lower run extending within said tank and movable upwardly along and above said inclined deck to a position above the body of liquid, said belt being provided with a plurality of transversely extending outwardly projecting rakes for moving settled solids upwardly along said deck; said belt extending transversely the major portion of the transverse extent of said rakes and being provided with a multiplicity of perforations distributed over its surface; and liquid spray means extending across said tank above the lower run of said belt and provided with spaced orifices so positioned and directed as to deliver a plurality of liquid sprays onto the upper surface of the belt at a position above the body of liquid and in a direction inclined downwardly and rearwardly with respect to the direction of travel of the belt, to wash solids from said upper surface through said perforations.

ALEXANDER C. MUNRO, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,205,326 Cole Nov. 12, 1916 2,196,119 Mitchell Apr. 2, 1940 

